In recent years, fibers that exhibit high shrink performance by means of heat treatment have been demanded in the development of high density woven fabrics. If a woven fabric produced by weaving such a highly shrinkable fiber is subjected to heat treatment, highly shrinkable fibers shrink, so that gaps between warps and wefts are reduced. As a result, a high density woven fabric that is appropriate in springiness, firmness, repellency and the like can be obtained.
Although highly shrinkable polyester filaments are used as such highly shrinkable fibers, they feel somewhat hard after being shrunk and therefore are problematic in comfortableness in clothing applications.
JP H03-64516 A discloses a highly shrinkable nylon fiber having a boiling water shrinkage of 15% or more. However, this fiber is designed for being fabricated into heterogeneously shrinkable combined filament yarn by being intermingled with another fiber. Therefore, if a woven fabric produced by weaving that fiber is subjected to heat treatment, it is not shrunk sufficiently due to its small shrinkage stress and a woven fabric having a high density could not be obtained.
JP H08-209444 A discloses a highly shrinkable nylon fiber having a boiling water shrinkage of 30% or more. However, since the polymer to be used for producing this fiber was produced by copolymerization, there have been a problem that the production of the copolymer requires time and labor and the cost becomes high.    Patent document 1: JP H03-64516 A    Patent document 2: JP H08-209444 A